Crankcase heaters are typically used in HVAC compressor applications. After prolonged off periods and before start up, refrigerant in compressors tend to mix with oil in the compressor forming a refrigerant/oil solution. A crankcase heater is used to drive out refrigerant from the refrigerant/oil solution in order to prevent damage to the compressor due to lack of lubrication and/or high solution volumes.
An effective crankcase heater which has become widely used is shown and described in U.S. Pat. No. 4,236,065. This heater device comprises a self-regulating positive temperature coefficient of resistivity (PTC) element potted inside a thermally conductive ceramic body, such as alumina or steatite. The ceramic body and PTC element are potted with grit (alumina powder and de-ionized water mixture) and then sealed with a sealant, such as RTV polymer, to seal the device from moisture. The ceramic body provides electrical isolation between the device and a metallic housing or well provided in the shell of a compressor which receives the heater device. Heat generated by the PTC element is conducted through the ceramic body and the metallic housing into the refrigerant/oil solution to boil off the refrigerant from the solution within the compressor. When heated, the PTC element increases in temperature to a preselected temperature based on the anomaly temperature or the Curie point of the PTC element.
However, due to tolerance stack-ups between the device and the inner well diameter, the ceramic body is required to be undersized so that it will fit into the metal well attached to the compressor housing. To augment heat transfer from the heater to the well, thermal joint compound such as thermal grease is used to fill the air pocket between the heater and the well. The inner diameter of the well determines the permissible outer diameter of the ceramic body which is to be fitted within the well. A heater device is installed by applying thermal grease on the device and in the well. The device is then inserted in the well and a retaining clip is inserted to secure the device in the well.
Although the above described heater device is reliable, long lasting and inexpensive, the installation procedure is more labor intensive and cumbersome than desired.